The present invention relates to the control of radio frequency (RF) signal power received in a multi band receiver. More particularly the invention relates to a method and apparatus for detection of interference energy from RF signals present in adjacent bandwidths and controlling the energy received in the baseband portion of the receiver to ensure that said baseband circuitry is not saturated or overdriven.
A dual mode communication device is designed to transmit and receive RF signals of either an analog or a digital nature. The method for transmitting analog RF signals is typically achieved using the advanced mobile phone system (AMPS) and the transmission method of digital RF signals may be chosen from a plurality of multiple access techniques including time division multiple access (TDMA), code division multiple access (CDMA), and global system for mobile communication (GSM). A multi mode device such as a dual mode device will combine some of these techniques and incorporate them into one device. The receiver portion of a dual mode communication device for example, is similar to those which are not dual mode but are adapted to receive a combination of signals in accordance with any two of the methods above, analog or digital.
Typical receiver circuitry comprises two general portions: a front end portion and a back end portion. The front end portion functions to perform initial filtering, amplification of the desired bandwidth, and conversion to an intermediate frequency for further processing by the backend portion of the receiver. The backend portion converts the signal to the baseband in preparation for digital signal processing. RF signals enter the front end portion via the antenna and are transferred from the front end to the back end.
Controlling the incoming signal power of a radio frequency receiver is essential to proper operation of the receiver as the control functions to maintain signal levels within the operating range of the baseband circuitry. If the signal level exceeds the operating range of said baseband circuitry, the receiver performance degrades as a result of the decreasing signal to noise ratio and receiver selectivity. This may occur when interfering adjacent signals are very strong compared to the desired on-channel signal and the baseband circuitry becomes saturated as a result of the overload. This results in the desired on-channel signal becoming desensitized. Therefore, it is necessary to control the received signal power prior to the baseband circuitry and maintain signal levels within the back end circuit""s operating range. Filter portions of the baseband circuitry reduce the adjacent interference noise signals by allowing only the desired on-channel frequency to pass through. However, the incoming aggregate power level prior to the baseband circuitry comprises the desired communication signal as well as the interfering noise energy. The combination of these two can lead to saturation of the baseband circuitry as a result of the noise level becoming too high.
One typical method of control is to provide measurement circuitry prior to the baseband circuitry such that a power estimation of the interfering noise level can be made. A conventional means for power estimation is to measure the aggregate received power level and provides measurement data to the received signal strength indicator (RSSI). The RSSI through additional circuitry, provides a control signal to the automatic gain control (AGC) corresponding to the estimated power level. The signal provided to the AGC from the RSSI is used to control the gain of the aggregate received power level entering the baseband circuitry. As the aggregate received power level increases, the AGC reduces the signal gain. This provides control of the incoming signal power but is performed with the disadvantages of additional cost of extra circuitry, increased integrated circuit (IC) size, and increased land requirement on the printed circuit board (PCB).
The use of additional circuitry poses a problem as this requires more space within the device and cost reduction is almost always desired. Therefore, there is a need to improve the means and method of detecting and controlling the noise entering the receiver.